In International patent specification No. WO 81/00588 there is described a method of manufacturing window and door frames from cored extruded plastics profiles in which the core material may be of high quality plywood or other suitable material (for example a cement-bonded fibrous material such as cement-bonded chipboard or cement-bonded glass fibres) provided with a cladding of plastics material e.g. polyvinylchloride.
For such frames the core material is required to possess a high degree of dimensional and shape stability and to be of adequate strength to bear the loads encountered by the frames in use in various weather conditions. Furthermore, as a timber substitute it may be desirable that the core material should possess good screw-holding properties.
In U.K. patent specification No. 2 028 406 B there is disclosed a method of manufacturing an extruded construction strip which is suitable for use in the manufacture of frames for windows and the like and which comprises a tubular section of thermosoftening plastics material (specifically PVC) filled with a matrix of methylmethacrylate with hollow silicate spherules as a filler. As described, the construction strip may incorporate within the matrix a number of filaments (specifically glass rovings) extending lengthwise of the strip for reinforcement purposes. In manufacturing the strip the plastics sheath forming the hollow section is extruded by a first extruding machine and the sheath is filled by extruding thereinto (by a second extruding machine) the plastics matrix of methylmethacrylate incorporating the silicate spherules, being extruded in the cold state into the hollow sheath whilst the latter is still hot. The glass rovings are drawn into the matrix during its extrusion by some means not disclosed. Curing of the matrix takes place as the strip is fed through a sizing bush of considerable length. It is apparent that the matrix must comprise a relatively high proportion of resin (methylmethacrylate) enabling the matrix to flow freely under pressure to fill the hollow section.
Furthermore, there is described in International patent specification No. WO 82/03243 a method of making somewhat similar structural profile, in which method: (i) a core comprising an unsaturated polyester resin incorporating a silicate filler and an additional mineral filler, thoroughly mixed and tightly compacted together, is extruded through a die, (ii) a sheath of a plastics material is extruded around the core, and (iii) the sheathed core is cured by means of heat, so as to effect curing of the core and cross-linking between the core and the sheath. The preferred silicate filler for that process, as described therein, is in the form of lightweight hollow microspheres, and an acrylic coating is preferred for the plastics sheath.
According to the process described in specification No. WO 82/03243, a very close packing of the selected fillers could be achieved, resulting in a considerable reduction in the amount of resin required. However, a further reduction in the resin content can be desirable. Furthermore, there could be an advantage in using, at least as the primary filler for the core of such structural profile, a readily-manufacturable material that could reduce the dependence on commercially supplied fillers.
There are known, and described for example in European patent specification No. 0 096 489 (A1), rigid inorganic foams of cellular structure comprising one or more layer minerals (hereinafter referred to as layer mineral foams). The term "layer minerals" includes vermiculite, kaolinite, kaolin-containing clays such as ball clays, china clays and fire clays, montmorillonite and sepiolite. Mixtures of layer minerals may be employed in making foams, as also may mixtures of one or more layer minerals with one or more materials other than layer minerals. Where the foam comprises at least a major proportion of clays (hereinafter referred to as a clay foam) it may be sintered to confer improved strength and water-stability.
Such rigid foams have been proposed for various uses, including insulation uses and the fire-protection of substrates. Whilst often produced in the form of extruded board or slab-stock, the foams are also produced in a coarse particulate extruded form known as prills, the prills comprising short extruded strands of the foam material. Production of such foams can be effected utilising readily available materials and relatively simple machinery.